Hi DigitalDude, and welcome to the Seven Forums
As it is limited to one share on one OS the only thing I can suggest is security permissions on the share assuming it is a NTFS drive - you may want to check that the users has sufficient effective permissions on the share files.
The other thing that may be causing an error is the Virtual CD
driver programs may have left a remnant registry entry or
driver DLL that is blocking the use of the drive letter you are assigning, (but that would not effect the UNC access, so not likely, but it's a BETA and weird things can happen

)
MagicDisk is particularly bad in leaving remnant
driver dll's so that may be a starting point